The ability to detect and identify explosives, drugs, chemical and biological agents as well as monitor air quality has become increasingly more critical given increasing terrorist and military activities and environmental concerns. Previous detection of such agents was accomplished with conventional mass spectrometers, time of flight (TOF) ion mobility spectrometers (IMS) and conventional field asymmetric ion mobility spectrometers (FAIMS), also known as differential mobility spectrometers (DMS).
Mass spectrometers (MS) are very sensitive and selective with fast response time. Mass spectrometers, however, are large and require significant amounts of power to operate. They also require a powerful vacuum pump to maintain a high vacuum in order to reduce ion neutral interactions and permit detection of the selected ions. Mass spectrometers are also very expensive.
Another spectrometric technique which is less complex is TOF IMS which is the method currently implemented in most portable chemical weapons and explosives detectors. The detection is based not solely on mass, but on charge and cross-section of the molecule as well. However, because of these different characteristics, molecular species identification is not as conclusive and accurate as the mass spectrometer. Time of flight ion mobility spectrometers typically have unacceptable resolution and sensitivity limitations when attempting to reduce their size. In time of flight ion mobility, the resolution is proportional to the length of the drift tube. The longer the tube the better the resolution, provided the drift tube is also wide enough to prevent all ions from being lost to the side walls due to diffusion. Thus, fundamentally, miniaturization of time of flight ion mobility systems leads to a degradation in system performance. While conventional time of flight devices are relatively inexpensive and reliable, they suffer from several limitations. First, the sample volume through the detector is small, so to increase spectrometer sensitivity either the detector electronics must have extremely high sensitivity, requiring expensive electronics, or a concentrator is required, adding to system complexity. In addition, a gate and gating electronics are usually needed to control the injection of ions into the drift tube.
FAIMS spectrometry, also known a differential mobility spectrometry (DMS), was developed in the former Soviet Union in the 1980's. FAIMS spectrometry allows a selected ion to pass through a filter while blocking the passage of undesirable ions. But the only commercial prior art FAIMS spectrometer was large and expensive, e.g., the entire device was nearly a cubic foot in size and cost over $25,000. Such systems are not suitable for use in applications requiring small detectors. They are also relatively slow, taking as much as one minute to produce a complete spectrum of the sample gas, are difficult to manufacture and are not mass producible.
The prior art FAIMS devices typically depend upon a carrier gas that flows in the same direction as the ion travel through the filter. However, the pumps required to draw the sample medium into the spectrometer and to provide a carrier gas can be rather large and can consume large amounts of power.
More recently, FAIMS systems have been implemented in compact micromachined form factors. Such relatively compact form factors have enabled reduced voltage, reduced power consumption, greater portability, longer battery lifetime, and greater integration flexibility. However, even smaller, ultra compact, form factors are desired to further improve the above advantages along with enabling a DMS to practically support additional applications.
One problem with certain micromachined FAIMS devices is the inability to maintain a pure, dehumidified, clean, or contamination free atmosphere within the filter. Certain multilayered micromachined FAIMS designs appear to be fundamentally flawed through the lack of control of purity of the supporting gas atmosphere and constancy of the same during use as a standalone analyzer with only a membrane inlet. Excursions in moisture will radically affect and degrade response and integrity of any analyzer response. Even the inclusion of molecular sieve components is problematic. Accordingly, there is a need to provide mechanisms that established a regulated and consistent atmosphere within certain multilayered micromachined filters.
Another problem is that ion mobility based systems, such as DMS or FAIMS, employ relatively inefficient, large form-factor, and high power-consuming power supplies to generate, for example, the asymmetric radio frequency (Vrf) and compensation (Vc or Vcomp) voltages that filter ions of a sample. In one example, a differential ion mobility spectrometer (DMS) may utilize over 13 watts to generate around a 1500 volt peak of Vrf. Thus, there is a need for enhanced generation and control designs which result in reduced system power consumption.